1. Field of the Invention
The present invention relates to a graphite base for heat sink and more particularly, to a method of making a graphite base by means of processing a graphite mixture of nanometered graphite and asphalt mixture into a graphite mass with a high pressure by means of hot press, cold press and vibration, and then dipping the graphite mass in a liquid phase asphalt, and then baking the graphite mass into a dry state graphite block.
2. Description of the Related Art
Following fast development of high technology, electronic devices are made in a mini scale, and element density in a unit area is relatively increased to enhance the working efficiency. An active electronic device produces much heat during operation. If heat is not quickly dissipated during the operation of an active electronic device, the electronic device will become unstable due to thermal stress or electron ionization. Therefore, it is important to prevent overheat of an electronic device during operation.
Because it is the market trend of semiconductor and electronic package toward high power and high density, heat dissipation problem will become more and more serious. For dissipating heat from electronic devices of high power density, pure copper is commonly used for making heat spreaders or heat pipes. However, copper heat spreaders and heat pipes are expensive. Further, the heat conductivity of copper and aluminum are about 400 W/mk and 200 W/mk respectively. These heat conductivities are not enough to dissipate heat from high-density power electronic devices efficiently. Further, copper and aluminum have a high density (about 8.5 g/cc and 2.7 g/cc respectively). A copper or aluminum heat sink has a certain weight, which gives a high pressure to the electronic device to which the heat sink is attached, such high pressure may damage the surface of the electronic device.
Because copper and aluminum-based heat sinks have the aforesaid drawbacks, new heat dissipation materials are desired. Further, carbon is an abundant natural substance in the world. When graphitized, carbon becomes a good electric and heat conductor. Natural graphite is a soft black material (see FIGS. 1 and 2). When natural graphite is rolled into a roll of thin sheet material, it has a high in-plane conductivity (about 240 W/M-K˜600 W/M-K), however its thru-thickness conductivity is still low (about 6 W/M). Therefore, graphite is commonly prepared in the form of a roll of thin sheet material but not made in the form of a block for application. Increasing the heat conductivity of graphite in vertical direction while maintaining its heat conductivity in horizontal direction is the key to the application of graphite in dissipation of heat.